The invention relates to an apparatus and method for extracting cataract tissue.
Every eye is divided into an anterior and posterior chamber by a normally transparent lens which focuses light onto the retina at the back of the posterior chamber. When the lens becomes cloudy for any of a variety of reasons, sight is impaired and the cloudy lens must be removed. Following removal of the lens, an intraocular lens (IOL) implant can be placed in the posterior chamber or thick glasses or contact lenses used to focus the light properly onto the retina.
A number of techniques are now in use for removing the cloudy cataract lens. In all these techniques a surgical tool is inserted into the eye through a small incision. Phacoemulsification is a recently developed technique which is being used more and more frequently. A small incision is made in the surface of the eye and a probe in the form of a rigid or semi-rigid tube inserted. This tube defines two internal paths-one for supplying an aspirating liquid, typically water, to the interior of the eye and a second to which a vacuum is connected for sucking out fragments of the cataract tissue and the aspirating liquid. Ultrasonic vibration is applied to the tube after the sharpened end is inserted by the surgeon into the cataract tissue. The ultrasonic vibration breaks up the cataract tissue which is aspirated together with the irrigating liquid.
One advantage of phacoemulsification is that the incision in the eye can be smaller than with other techniques. A smaller incision stabilizes the refractive error sooner and reduces the amount of induced post operative astigmatism. Of course that advantage is lost if the incision must be lengthened to insert the IOL. However, the present development of small incision intraocular lenses and the future possibility of in sito formation of lenses by injection of polymer into the intact capsular bag make phacoemulsification particularly attractive since with these techniques the incision need not be increased beyond the initial 2.5-3.5 millimeters required for phacoemulsification.
One difficulty with phacoemulsification is that considerable problems are often encountered in mastering the skills needed to perform the procedure safely. Further, occasional difficulties arise in removing all of the cataract tissue. In addition the sharp point of the probe can inadvertently damage delicate eye tissues.
Laser radiation has for the past several years been used to ablate various tissues within the eye. For example, the use of a ND:YAG laser (hereinafter referred to by the more common term, YAG laser) to remove abnormal and normal tissue has been explored, for example, see the patent to Krasnov, U.S. Pat. No. 3,971,382; U.S. application Ser. No. 702,569 filed Feb. 19, 1985; and an article by William Steven Chambles entitled Neodymium: YAG Laser Anterior Capsulotomy And A Possible New Application, (AM Intra-Ocular Implant Society Journal, Vol. 11, January 1985). It has generally been recognized that laser radiation, particularly from a YAG laser, will soften cataract tissue.
However, one of the difficulties with the use of laser radiation to soften cataract tissue is that the fragments of the tissue are often too large or otherwise dimensioned to pass readily through an aspirating opening in a probe such as used in phacoemulsification. In order to avoid making the incision more than the desired 2.5-3.5 millimeters, the aspirating opening must necessarily be quite small and the dimensions of the path within the probe to the vacuum source similarly restricted. For that and other reasons, the use of laser radiation to soften cataracts for subsequent aspiration has not been practical as a standard surgical procedure.